Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true, and openWorldHint=true, so the safety profile is covered. The description adds two things annotations cannot: the manage-token authorization requirement and the fact that the currency can be set before the event is ever tracked. It does not clarify what the 'destructive' overwrite of an existing currency value actually does, which is the one remaining gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two front-loaded sentences that state action, timing, and auth before trailing the raw endpoint. Tight overall, though the endpoint string and the restatement of the verb from the title add little for an agent.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 3-required-param mutation with no output schema, the description covers the action, the identifier, the auth requirement, and the notable pre-tracking timing. Annotations carry the rest of the behavioral surface; only the effect of overwriting an existing currency is unstated, which is a minor gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so site_id, event_name, and currency (with its full enum) are already well documented in the schema. The description only restates 'by event name' and adds no format, casing, or selection nuance beyond what the schema provides, matching the baseline 3 for high-coverage schemas.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (set), resource (an event's currency/value), and the selector (by event name), which clearly distinguishes it from the sibling fathom_clear_event_currency, even though that sibling is not named explicitly. It also adds the pre-tracking scope, so an agent knows what this does without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a real usage condition — 'works before the event is first tracked' — and the prerequisite 'Needs a manage token for the site', which tells the agent when it can act. It stops short of explicitly contrasting with fathom_clear_event_currency or stating when not to use this tool, so it is clear context rather than full when/when-not guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.